From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B9B92C19F2B for ; Wed, 3 Aug 2022 04:21:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232665AbiHCEUJ (ORCPT ); Wed, 3 Aug 2022 00:20:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230239AbiHCEUI (ORCPT ); Wed, 3 Aug 2022 00:20:08 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A0FF2B60B; Tue, 2 Aug 2022 21:20:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B958A612E4; Wed, 3 Aug 2022 04:20:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84062C433D6; Wed, 3 Aug 2022 04:20:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1659500406; bh=4XvW6Am+LFtU+beJUyoqbF5SdzyM95956jiHnqhMtGw=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=fP7OAmnJdeDrH+3lKsGs+j7tgGMMLB/DbAh9jWp67VxaRsmO7QibW7knm2D2iYqZG dSVQlg7tWQQjiQP2uvEepCh5ML010EhvEJDE6rnIBneJxT3mWexptkIVMdxHaAV9PK 0GEngfIwWPmIHP8Fi2aou9E21t9PuJdIKKksaZuqUSdy5tBFXAiPLM3QVzxB6rTWH8 uLbLhTU3bzqlWeg5Q8xKUlmlh6Owbdvf+LjbUXbJDiTCYyWephMAaEvGelYdg7GiDO OlG7AH4mP60rel0pO+jvwR0Jy/ng+Vz0sYXEMcntQ2SgFkrnZdDl4V69RvYnSuPOMD 02P7prfEmDn8g== Message-ID: <9e8728e0-75e7-d3a8-038b-48e51be4df07@kernel.org> Date: Tue, 2 Aug 2022 22:20:04 -0600 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH] net: seg6: initialize induction variable to first valid array index Content-Language: en-US To: Nick Desaulniers , Hideaki YOSHIFUJI , "David S. Miller" Cc: Thomas Gleixner , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Nathan Chancellor , Tom Rix , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Andrea Mayer References: <20220802161203.622293-1-ndesaulniers@google.com> From: David Ahern In-Reply-To: <20220802161203.622293-1-ndesaulniers@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ cc Andrea ] On 8/2/22 10:12 AM, Nick Desaulniers wrote: > Fixes the following warnings observed when building > CONFIG_IPV6_SEG6_LWTUNNEL=y with clang: > > net/ipv6/seg6_local.o: warning: objtool: seg6_local_fill_encap() falls > through to next function seg6_local_get_encap_size() > net/ipv6/seg6_local.o: warning: objtool: seg6_local_cmp_encap() falls > through to next function input_action_end() > > LLVM can fully unroll loops in seg6_local_get_encap_size() and > seg6_local_cmp_encap(). One issue in those loops is that the induction > variable is initialized to 0. The loop iterates over members of > seg6_action_params, a global array of struct seg6_action_param calling > their put() function pointer members. seg6_action_param uses an array > initializer to initialize SEG6_LOCAL_SRH and later elements, which is > the third enumeration of an anonymous union. > > The guard `if (attrs & SEG6_F_ATTR(i))` may prevent this from being > called at runtime, but it would still be UB for > `seg6_action_params[0]->put` to be called; the unrolled loop will make > the initial iterations unreachable, which LLVM will later rotate to > fallthrough to the next function. > > Make this more obvious that this cannot happen to the compiler by > initializing the loop induction variable to the minimum valid index that > seg6_action_params is initialized to. > > Reported-by: Thomas Gleixner > Signed-off-by: Nick Desaulniers > --- > net/ipv6/seg6_local.c | 10 +++++----- > 1 file changed, 5 insertions(+), 5 deletions(-) > > diff --git a/net/ipv6/seg6_local.c b/net/ipv6/seg6_local.c > index 2cd4a8d3b30a..b7de5e46fdd8 100644 > --- a/net/ipv6/seg6_local.c > +++ b/net/ipv6/seg6_local.c > @@ -1614,7 +1614,7 @@ static void __destroy_attrs(unsigned long parsed_attrs, int max_parsed, > * callback. If the callback is not available, then we skip to the next > * attribute; otherwise, we call the destroy() callback. > */ > - for (i = 0; i < max_parsed; ++i) { > + for (i = SEG6_LOCAL_SRH; i < max_parsed; ++i) { > if (!(parsed_attrs & SEG6_F_ATTR(i))) > continue; > > @@ -1643,7 +1643,7 @@ static int parse_nla_optional_attrs(struct nlattr **attrs, > struct seg6_action_param *param; > int err, i; > > - for (i = 0; i < SEG6_LOCAL_MAX + 1; ++i) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; ++i) { > if (!(desc->optattrs & SEG6_F_ATTR(i)) || !attrs[i]) > continue; > > @@ -1742,7 +1742,7 @@ static int parse_nla_action(struct nlattr **attrs, struct seg6_local_lwt *slwt) > } > > /* parse the required attributes */ > - for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) { > if (desc->attrs & SEG6_F_ATTR(i)) { > if (!attrs[i]) > return -EINVAL; > @@ -1847,7 +1847,7 @@ static int seg6_local_fill_encap(struct sk_buff *skb, > > attrs = slwt->desc->attrs | slwt->parsed_optattrs; > > - for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) { > if (attrs & SEG6_F_ATTR(i)) { > param = &seg6_action_params[i]; > err = param->put(skb, slwt); > @@ -1927,7 +1927,7 @@ static int seg6_local_cmp_encap(struct lwtunnel_state *a, > if (attrs_a != attrs_b) > return 1; > > - for (i = 0; i < SEG6_LOCAL_MAX + 1; i++) { > + for (i = SEG6_LOCAL_SRH; i < SEG6_LOCAL_MAX + 1; i++) { > if (attrs_a & SEG6_F_ATTR(i)) { > param = &seg6_action_params[i]; > if (param->cmp(slwt_a, slwt_b))